I own a copy of that. Most of those rituals require a massive amount of other trinkets (like silver with the deity's name engraved into it by your own hand, left in total darkness and wrapped in silk - then placed in the moon light every night in order to absorb the lunar energies of Sin-Nanna).
If he so happened to have called upon one of them, he probably didn't read all the warnings and other points of how to perform the rituals at the very back of the book. If anything, the spirit is probably not even the proper spirit he called forth from beyond the gates (There are so many stories of this occurring, it isn't even funny), because those formulas are very specific and tend to be very potent... don't forget calling upon those particular spirits at the proper time of the day, the specific days of the year, etc.
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